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The Compton Effect

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The Compton Effect is the phenomenon of the decrease in energy of photon when scattered by a free charged particle.

Learning Objectives

Explain why Compton scattering is an inelastic scattering.

Describe process of Compton scattering.

Discuss importance of the Compton effect.

Key Points

Compton scattering is an example of inelastic scattering because the wavelength of the scattered light is different from the incident radiation.

Like the photoelectric effects, the Compton effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon.
Light must behave as if it consists of particles to explain the Compton scattering.

Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (quanta) whose energy is proportional to the frequency.

an elastic scattering of electromagnetic radiation by a free charged particle, as described by classical electromagnetism.
It is just the low-energy limit of Compton scattering

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Full Text

The Compton Effect

Compton scattering is an inelastic scattering of a photon by a free charged particle (usually an electron, ).
It results in a decrease in energy (increase in wavelength) of the photon (which may be an X-ray or gamma ray photon), called the Compton Effect.
Part of the energy of the photon is transferred to the scattering electron.
Inverse Compton scattering also exists, and happens when a charged particle transfers part of its energy to a photon.

The Compton Effect is the name given to the scattering of a photon by an electron.
Energy and momentum are conserved, resulting in a reduction of both for the scattered photon.
Studying this effect, Compton verified that photons have momentum.

Compton scattering is an example of inelastic scattering because the wavelength of the scattered light is different from the incident radiation.
Still, the origin of the effect can be considered as an elastic collision between a photon and an electron.
The amount of change in the wavelength is called the Compton shift.
Although nuclear Compton scattering exists, Compton scattering usually refers to the interaction involving only the electrons of an atom.

The Compton effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon.
Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shifts in wavelength: classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light.
However, the effect will become arbitrarily small at sufficiently low light intensities regardless of wavelength.
Light must behave as if it consists of particles to explain the low-intensity Compton scattering.
Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (quanta) whose energy is proportional to the frequency.

wavelength of the scattered light is identical to the wavelength of the incident radiation, angle of the scattered light is different from the incident radiation, color of the scattered light is identical to the color of the incident radiation, and wavelength of the scattered light is different from the incident radiation

elastic scattering of a photon by a free charged particle, inelastic scattering of a phonon by a free charged particle, elastic scattering of an electron by an atom, and inelastic scattering of a photon by a free charged particle